$ { \left[\begin{array}{rr}{2} & {3} \\ {-1} & {1} \\ {3} & {1}\end{array}\right]+\left[\begin{array}{rr}{-1} & {0} \\ {0} & {-1} \\ {3} & {-1}\end{array}\right] = {?} } $
Solution: To find the sum of two matrices, add the corresponding items between each matrix. ${\left[\begin{array}{rr}{2}+{-1} & {3}+{0} \\ {-1}+{0} & {1}+{-1} \\ {3}+{3} & {1}+{-1}\end{array}\right]}$ Now, simplify: ${\left[\begin{array}{rr}{1} & {3} \\ {-1} & {0} \\ {6} & {0}\end{array}\right]}$